| Message ID | 1465854326-19160-3-git-send-email-rth@twiddle.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 13 June 2016 at 22:45, Richard Henderson <rth@twiddle.net> wrote: > Signed-off-by: Richard Henderson <rth@twiddle.net> > --- > linux-user/host/i386/hostdep.h | 34 ++++++++++ > linux-user/host/i386/safe-syscall.inc.S | 110 ++++++++++++++++++++++++++++++++ > 2 files changed, 144 insertions(+) > create mode 100644 linux-user/host/i386/hostdep.h > create mode 100644 linux-user/host/i386/safe-syscall.inc.S > > diff --git a/linux-user/host/i386/hostdep.h b/linux-user/host/i386/hostdep.h > new file mode 100644 > index 0000000..9e2b4d7 > --- /dev/null > +++ b/linux-user/host/i386/hostdep.h > @@ -0,0 +1,34 @@ > +/* > + * hostdep.h : things which are dependent on the host architecture > + * > + * This work is licensed under the terms of the GNU GPL, version 2 or later. > + * See the COPYING file in the top-level directory. > + */ > + > +#ifndef QEMU_HOSTDEP_H > +#define QEMU_HOSTDEP_H > + > +/* We have a safe-syscall.inc.S */ > +#define HAVE_SAFE_SYSCALL > + > +#ifndef __ASSEMBLER__ > + > +/* These are defined by the safe-syscall.inc.S file */ > +extern char safe_syscall_start[]; > +extern char safe_syscall_end[]; > + > +/* Adjust the signal context to rewind out of safe-syscall if we're in it */ > +static inline void rewind_if_in_safe_syscall(void *puc) > +{ > + struct ucontext *uc = puc; > + greg_t *pcreg = &uc->uc_mcontext.gregs[REG_EIP]; user-exec.c has #ifndef REG_EIP /* for glibc 2.1 */ #define REG_EIP EIP #endif Do we still care about glibc 2.1 ? (Probably not, 2.2 was released fifteen years ago now...) > + > + if (*pcreg > (uintptr_t)safe_syscall_start > + && *pcreg < (uintptr_t)safe_syscall_end) { > + *pcreg = (uintptr_t)safe_syscall_start; > + } > +} > + > +#endif /* __ASSEMBLER__ */ > + > +#endif > diff --git a/linux-user/host/i386/safe-syscall.inc.S b/linux-user/host/i386/safe-syscall.inc.S > new file mode 100644 > index 0000000..f5f0c64 > --- /dev/null > +++ b/linux-user/host/i386/safe-syscall.inc.S > @@ -0,0 +1,110 @@ > +/* > + * safe-syscall.inc.S : host-specific assembly fragment > + * to handle signals occurring at the same time as system calls. > + * This is intended to be included by linux-user/safe-syscall.S Missing copyright/written by attribution ? > + * > + * This work is licensed under the terms of the GNU GPL, version 2 or later. > + * See the COPYING file in the top-level directory. > + */ > + > + .global safe_syscall_base > + .global safe_syscall_start > + .global safe_syscall_end > + .type safe_syscall_base, @function I guess 4-space indent would match the rest of QEMU... > + > + /* This is the entry point for making a system call. The calling > + * convention here is that of a C varargs function with the > + * first argument an 'int *' to the signal_pending flag, the > + * second one the system call number (as a 'long'), and all further > + * arguments being syscall arguments (also 'long'). > + * We return a long which is the syscall's return value, which > + * may be negative-errno on failure. Conversion to the > + * -1-and-errno-set convention is done by the calling wrapper. > + */ > +safe_syscall_base: > + .cfi_startproc > + push %ebp > + .cfi_adjust_cfa_offset 4 > + .cfi_rel_offset ebp, 0 > + push %esi > + .cfi_adjust_cfa_offset 4 > + .cfi_rel_offset esi, 0 > + push %edi Odd indentation here. > + .cfi_adjust_cfa_offset 4 > + .cfi_rel_offset edi, 0 > + push %ebx > + .cfi_adjust_cfa_offset 4 > + .cfi_rel_offset ebx, 0 > + > + /* The syscall calling convention isn't the same as the C one: > + * we enter with 0(%esp) == return address > + * 4(%esp) == *signal_pending > + * 8(%esp) == syscall number > + * 12(%esp) ... 32(%esp) == syscall arguments > + * and return the result in eax > + * and the syscall instruction needs > + * eax == syscall number > + * ebx, ecx, edx, esi, edi, ebp == syscall arguments > + * and returns the result in eax > + * Shuffle everything around appropriately. > + * Note the 16 bytes that we pushed to save registers. > + */ > + mov 12+16(%esp), %ebx /* the syscall arguments */ > + mov 16+16(%esp), %ecx > + mov 20+16(%esp), %edx > + mov 24+16(%esp), %esi > + mov 28+16(%esp), %edi > + mov 32+16(%esp), %ebp > + > + /* This next sequence of code works in conjunction with the > + * rewind_if_safe_syscall_function(). If a signal is taken > + * and the interrupted PC is anywhere between 'safe_syscall_start' > + * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. > + * The code sequence must therefore be able to cope with this, and > + * the syscall instruction must be the final one in the sequence. > + */ > +safe_syscall_start: > + /* if signal_pending is non-zero, don't do the call */ > + mov 4+16(%esp), %eax /* signal_pending */ > + cmp $0, (%eax) > + mov 8+16(%esp), %eax /* syscall number */ > + jnz 1f Any particular reason for doing the jump after the mov? > + int $0x80 > +safe_syscall_end: > + /* code path for having successfully executed the syscall */ > + pop %ebx > + .cfi_remember_state > + .cfi_def_cfa_offset 4 Shouldn't these all be ".cfi_adjust_cfa_offset -4" ? That's what glibc uses AFAICT. > + .cfi_restore ebx > + pop %edi > + .cfi_def_cfa_offset 4 > + .cfi_restore edi > + pop %esi > + .cfi_def_cfa_offset 4 > + .cfi_restore esi > + pop %ebp > + .cfi_def_cfa_offset 4 > + .cfi_restore ebp > + ret > + > +1: > + /* code path when we didn't execute the syscall */ > + .cfi_restore_state > + mov $-TARGET_ERESTARTSYS, %eax > + pop %ebx > + .cfi_remember_state We don't need to remember state here I think. > + .cfi_def_cfa_offset 4 > + .cfi_restore ebx > + pop %edi > + .cfi_def_cfa_offset 4 > + .cfi_restore edi > + pop %esi > + .cfi_def_cfa_offset 4 > + .cfi_restore esi > + pop %ebp > + .cfi_def_cfa_offset 4 > + .cfi_restore ebp > + ret > + .cfi_endproc > + > + .size safe_syscall_base, .-safe_syscall_base > -- > 2.5.5 Other than some trivialities like order of register push/pops this is virtually identical code to the version I had, so it must be right :-) thanks -- PMM
On 06/14/2016 04:58 AM, Peter Maydell wrote: >> + greg_t *pcreg = &uc->uc_mcontext.gregs[REG_EIP]; > > user-exec.c has > #ifndef REG_EIP > /* for glibc 2.1 */ > #define REG_EIP EIP > #endif > > Do we still care about glibc 2.1 ? (Probably not, 2.2 was > released fifteen years ago now...) > Heh. I would say not. We've got other much more recent requirements. >> + * >> + * This work is licensed under the terms of the GNU GPL, version 2 or later. >> + * See the COPYING file in the top-level directory. >> + */ >> + >> + .global safe_syscall_base >> + .global safe_syscall_start >> + .global safe_syscall_end >> + .type safe_syscall_base, @function > > I guess 4-space indent would match the rest of QEMU... This is assembler not C. My brain is tied to a 1-tab indent. >> + .cfi_rel_offset esi, 0 >> + push %edi > > Odd indentation here. Yeah, that's mixing code from your x86_64 version which uses spaces not tabs. >> + cmp $0, (%eax) >> + mov 8+16(%esp), %eax /* syscall number */ >> + jnz 1f > > Any particular reason for doing the jump after the mov? No. Indeed, recent cpus will fuse the cmp+jnz so they're better off together. >> + .cfi_def_cfa_offset 4 > > Shouldn't these all be ".cfi_adjust_cfa_offset -4" ? That's what glibc > uses AFAICT. Typo. Good catch. >> + .cfi_remember_state > > We don't need to remember state here I think. Correct. Cut and paste. > Other than some trivialities like order of register push/pops > this is virtually identical code to the version I had, so it > must be right :-) Heh. r~
diff --git a/linux-user/host/i386/hostdep.h b/linux-user/host/i386/hostdep.h new file mode 100644 index 0000000..9e2b4d7 --- /dev/null +++ b/linux-user/host/i386/hostdep.h @@ -0,0 +1,34 @@ +/* + * hostdep.h : things which are dependent on the host architecture + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ + +#ifndef QEMU_HOSTDEP_H +#define QEMU_HOSTDEP_H + +/* We have a safe-syscall.inc.S */ +#define HAVE_SAFE_SYSCALL + +#ifndef __ASSEMBLER__ + +/* These are defined by the safe-syscall.inc.S file */ +extern char safe_syscall_start[]; +extern char safe_syscall_end[]; + +/* Adjust the signal context to rewind out of safe-syscall if we're in it */ +static inline void rewind_if_in_safe_syscall(void *puc) +{ + struct ucontext *uc = puc; + greg_t *pcreg = &uc->uc_mcontext.gregs[REG_EIP]; + + if (*pcreg > (uintptr_t)safe_syscall_start + && *pcreg < (uintptr_t)safe_syscall_end) { + *pcreg = (uintptr_t)safe_syscall_start; + } +} + +#endif /* __ASSEMBLER__ */ + +#endif diff --git a/linux-user/host/i386/safe-syscall.inc.S b/linux-user/host/i386/safe-syscall.inc.S new file mode 100644 index 0000000..f5f0c64 --- /dev/null +++ b/linux-user/host/i386/safe-syscall.inc.S @@ -0,0 +1,110 @@ +/* + * safe-syscall.inc.S : host-specific assembly fragment + * to handle signals occurring at the same time as system calls. + * This is intended to be included by linux-user/safe-syscall.S + * + * This work is licensed under the terms of the GNU GPL, version 2 or later. + * See the COPYING file in the top-level directory. + */ + + .global safe_syscall_base + .global safe_syscall_start + .global safe_syscall_end + .type safe_syscall_base, @function + + /* This is the entry point for making a system call. The calling + * convention here is that of a C varargs function with the + * first argument an 'int *' to the signal_pending flag, the + * second one the system call number (as a 'long'), and all further + * arguments being syscall arguments (also 'long'). + * We return a long which is the syscall's return value, which + * may be negative-errno on failure. Conversion to the + * -1-and-errno-set convention is done by the calling wrapper. + */ +safe_syscall_base: + .cfi_startproc + push %ebp + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset ebp, 0 + push %esi + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset esi, 0 + push %edi + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset edi, 0 + push %ebx + .cfi_adjust_cfa_offset 4 + .cfi_rel_offset ebx, 0 + + /* The syscall calling convention isn't the same as the C one: + * we enter with 0(%esp) == return address + * 4(%esp) == *signal_pending + * 8(%esp) == syscall number + * 12(%esp) ... 32(%esp) == syscall arguments + * and return the result in eax + * and the syscall instruction needs + * eax == syscall number + * ebx, ecx, edx, esi, edi, ebp == syscall arguments + * and returns the result in eax + * Shuffle everything around appropriately. + * Note the 16 bytes that we pushed to save registers. + */ + mov 12+16(%esp), %ebx /* the syscall arguments */ + mov 16+16(%esp), %ecx + mov 20+16(%esp), %edx + mov 24+16(%esp), %esi + mov 28+16(%esp), %edi + mov 32+16(%esp), %ebp + + /* This next sequence of code works in conjunction with the + * rewind_if_safe_syscall_function(). If a signal is taken + * and the interrupted PC is anywhere between 'safe_syscall_start' + * and 'safe_syscall_end' then we rewind it to 'safe_syscall_start'. + * The code sequence must therefore be able to cope with this, and + * the syscall instruction must be the final one in the sequence. + */ +safe_syscall_start: + /* if signal_pending is non-zero, don't do the call */ + mov 4+16(%esp), %eax /* signal_pending */ + cmp $0, (%eax) + mov 8+16(%esp), %eax /* syscall number */ + jnz 1f + int $0x80 +safe_syscall_end: + /* code path for having successfully executed the syscall */ + pop %ebx + .cfi_remember_state + .cfi_def_cfa_offset 4 + .cfi_restore ebx + pop %edi + .cfi_def_cfa_offset 4 + .cfi_restore edi + pop %esi + .cfi_def_cfa_offset 4 + .cfi_restore esi + pop %ebp + .cfi_def_cfa_offset 4 + .cfi_restore ebp + ret + +1: + /* code path when we didn't execute the syscall */ + .cfi_restore_state + mov $-TARGET_ERESTARTSYS, %eax + pop %ebx + .cfi_remember_state + .cfi_def_cfa_offset 4 + .cfi_restore ebx + pop %edi + .cfi_def_cfa_offset 4 + .cfi_restore edi + pop %esi + .cfi_def_cfa_offset 4 + .cfi_restore esi + pop %ebp + .cfi_def_cfa_offset 4 + .cfi_restore ebp + ret + .cfi_endproc + + .size safe_syscall_base, .-safe_syscall_base
Signed-off-by: Richard Henderson <rth@twiddle.net> --- linux-user/host/i386/hostdep.h | 34 ++++++++++ linux-user/host/i386/safe-syscall.inc.S | 110 ++++++++++++++++++++++++++++++++ 2 files changed, 144 insertions(+) create mode 100644 linux-user/host/i386/hostdep.h create mode 100644 linux-user/host/i386/safe-syscall.inc.S